Elastic fixing roller and method of producing the same

ABSTRACT

A fixing roller for use in the fixing stage of a fixing apparatus such as a copying machine provided with multiple rubber and/or fabric layers of certain thicknesses and hardnesses surrounding a core member to improve the copying characteristics of the roller.

This is a division of application Ser. No. 07/259,729, filed 10/19/88,now U.S. Pat. No. 4,887,394.

FIELD OF THE INVENTION

The present invention relates to a fixing roller for use in the fixingstage or copying machines, facsimile equipment, line printers and likesystems. More particularly, the fixing roller of the present inventionis provided with multiple rubber and/or fabric layers of certainthicknesses and hardnesses surrounding a core member to improve thecopying characteristics of the roller.

BACKGROUND OF THE INVENTION

In a typical fixing apparatus, such as a copying machine, a piece ofcopy paper having an unfixed toner picture adhered thereto is passedbetween rubber heating and pressing rollers to fix the toner picture tothe copy paper. However, numerous problems are associated with the useof conventional rubber fixing rollers which are commonly coated with afluorocarbon resin. Because the resin has no elasticity, the heatingroller tends to crush the toner, thereby lowering the picture quality ofthe copy. Lack of elasticity also lowers the heat conductivity of theroller resulting in poor toner fixing, a particular problem inhigh-speed copying machines. A roller that lacks elasticity also tendsto wrinkle the copy paper.

A heating roller coated with a heat-resistant rubber also createsproblems in the copying process. The separating pawls of the copyingmachine often damage the rubber coating when a copier becomes jammedwith paper, thereby shortening roller life. Further, such a roller haspoor toner releasing properties which tends to offset the toner and,thus, lower the picture quality of the copy.

Unexamined Japanese Patent Publication No. 60-179770 [hereinafterreferred to as the Japanese Publication], filed by the same applicantherein, discloses improving the useful life of rubber rollers by using arubber layer of porous ethylene tetrafluoride resin impregnated withliquid silicone rubber.

The roller disclosed in the Japanese Publication, however, also hasproblems associated with its use. One such problem concerns the rubberhardness which cannot be made with less than a Shore hardness of 50degrees and, consequently, is too high. Also, because of polishing, theroller surface has uneven portions of several micrometers resulting inreduced toner releasing properties, particularly when the roller is usedfor color copying and like processes. In that case, the rollerpreferably has a mirrored surface to produce a glossy picture.Furthermore, when a porous material such as ethylene tetrafluoride resinis used to coat the roller, it is impossible to impregnate the pores ofthe material with a liquid rubber having a high viscosity (10,000 c.s.or more) generally used in a liquid injection molding system (LIMS).This is because the pore diameter is very fine, about 20 μm at the most,which limits the quantity of filler that can be used to improve thecopying characteristics of the roller.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a fixing roller thatsolves the foregoing problems in the prior art and to provide a methodfor producing such a roller. To attain that object, according to a firstembodiment of the present invention, the fixing roller comprises aroller core; a first heat-resistant rubber layer provided on an outersurface of the roller core; a second heat-resistant rubber layerprovided on the outer surface of the first heat-resistant rubber layer,the second heat-resistant rubber layer being reinforced at its outersurface by a heat-resistant porous material; and a thin thirdheat-resistant rubber layer provided on the outer surface of the secondheat-resistant rubber layer.

A method of producing the first embodiment of the fixing roller of thepresent invention involves the steps of setting the heat-resistantporous material inside a metal mold having a mirror-finished innersurface; setting the roller core at the center of the mold; pouringliquid rubber between the roller core and the porous material toimpregnate the porous material with the liquid rubber; and removing thecontents of the mold after hardening.

Another method of producing the first embodiment of the fixing roller ofthe present invention involves the steps of providing a heat-resistantrubber layer on the outer surface of the roller core; coating theheat-resistant rubber layer with a heat-resistant porous material;impregnating the heat-resistant porous material with liquid rubber;hardening the liquid rubber; polishing the resultant roller to improveits roundness; and forming a thin heat-resistant rubber coating film onthe outside of the polished roller using a liquid phase method.

A second embodiment of the elastic fixing roller of the presentinvention comprises a roller base member similar to that disclosed inthe Japanese Publication having a porous layer of fluorocarbon resinprovided on the outer surface of the roller base member, the porousmaterial having porous portions impregnated with heat-resistant liquidrubber, the liquid rubber being hardened after impregnation. To enlargethe pore size of the porous portions, the porous material is formed byextending and baking the fluorocarbon resin filled with an inorganicfiller having a particle size no larger than 5 μm. The liquid rubbercontains an inorganic filler and/or a releasing agent to provide theroller with heat resistance, heat conductivity, electrical conductivity,and releasing properties.

A third embodiment of the elastic fixing roller of the present inventioncomprises a roller core; a layer provided on the outer surface of theroller core made of a reinforcing heat-resistant material impregnatedwith a reinforcing heat-resistant elastic material that is hardenedafter impregnation; and a thin film of a heat-resistant elastic materialprovided on the outer surface of the heat-resistant layer.

A fourth embodiment of the elastic fixing roller of the presentinvention comprises a roller core and a layer provided on the outersurface of the roller core made of either a woven or nonwoven fabric ofheat-resistant fibers, the selected fabric being impregnated with liquidheat-resistant rubber and then hardened.

A fifth embodiment of the elastic fixing roller of the present inventioncomprises a roller core; a first heat-resistant rubber layer provided onthe outer surface of the roller core; and a second heat-resistant rubberlayer provided on the outer surface of the first heat-resistant rubberlayer, the second heat-resistant rubber layer being reinforced by eithera heat-resistant porous material or heat-resistant fibers exposed at theouter surface of the second heat-resistant rubber layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a fixing stage of a fixingapparatus;

FIG. 2 is a cross-sectional view of an elastic fixing roller accordingto a first embodiment of the present invention;

FIG. 3 is a cross-sectional view of a mold for producing an elasticfixing roller according to the first embodiment of the presentinvention;

FIG. 4 is a cross-sectional view of a fixing apparatus employing theelastic fixing roller of FIG. 2;

FIG. 5 is a cross-sectional view showing an elastic fixing rolleraccording to a second embodiment of the present invention;

FIG. 6 is a cross-sectional view showing a fixing apparatus employingthe elastic fixing roller of FIG. 5;

FIG. 7 is a cross-sectional view showing an elastic fixing rolleraccording to a third embodiment of the present invention;

FIG. 8 is a cross-sectional view of a fixing apparatus employing theelastic fixing roller of FIG. 7;

FIG. 9 is a cross-sectional view showing the elastic fixing rolleraccording to a fourth embodiment of the present invention;

FIG. 10 is a cross-sectional view showing a fixing apparatus employingthe elastic fixing roller of FIG. 9;

FIG. 11 is a cross-sectional view showing the elastic fixing rolleraccording to a fifth embodiment of the present invention; and

FIG. 12 is a cross-sectional view showing a fixing apparatus using theelastic fixing roller of FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a typical fixing stage 1 of a copying machine. Copy paper13 having an unfixed picture of toner 12 transferred thereon is passedbetween a set of fixing rollers comprising a heating roller 10 and apressing roller 11. A heater 23, located inside the core 14 of roller10, provides a source of heat for roller 10. The heat generated byroller 10, generally in the range of 170°-200° C., and the pressureexerted by roller 11 fix toner 12 onto copy paper 13 resulting in afixed picture 20.

Heating roller 10 is formed with a roller base member or core 14 whichcan be manufactured from ceramics, plastics, or a metal material such asaluminum. To increase the releasing properties of the toner, the surfaceof roller core 14 is provided with a coating 15 of fluorocarbon resinseveral tens μm thick or with a coating of silicone rubber orfluororubber having a thickness of 1 mm or less. Pressing roller 11 isformed with an aluminum roller core 16 having a coating 17 ofheat-resistant rubber, such as silicone rubber, several millimetersthick having a Shore hardness of ten degrees.

FIG. 1 further shows separating pawls 18 each having a width of severalmillimeters attached at four or five portions to prevent copy paper 13from winding around the roller. Separating pawls 18 generally areprovided only on the heating roller. However, in a high-speed copyingmachine, or an automatic double-surface copying machine separating pawlsare provided on both the heating and pressing rollers, as shown in FIG.1.

FIGS. 2 and 3 represent a first embodiment of the present invention. Asshown in FIG. 2, the elastic fixing roller has a roller core 101 made ofa metal, ceramic, plastic, or the like. A heat-resistant rubber layer102 is provided on the outer surface of roller core 101. A secondheat-resistant rubber layer 104, reinforced by a heat-resistant porousmaterial 103 such as, for example, a porous tube of fluorocarbon resinor the like, is formed on the outer surface of rubber layer 102. Theoutermost layer of the roller is a thin heat-resistant rubber layer 105,preferably 0.2 mm or less in thickness. Rubber layer 105 may be formedby monobloc molding using a metal mold or by a liquid phase method aftergrinding.

The heat-resistant rubber may contain an inorganic filler to raise itsheat-resistance and electrical conductivity. In addition, a silicone oilmay be added to the heat-resistant rubber to raise its releasingproperties.

The elastic fixing roller according to the first embodiment of thepresent invention, as well as the other embodiments to be described, canbe used either as a heating or pressing roller or as a roller that mustbe heat-resistant.

FIG. 3 illustrates a method for manufacturing the elastic fixing rolleraccording to the first embodiment of the present invention. First, theheat-resistant porous material 103 is set inside a hollow metal mold 130having a mirrored inner surface, and roller core 101 is set at thecenter of mold 130 atop a metal roller core fitting 132. Liquid rubber131, for example, silicone rubber or the like, is poured between rollercore 101 and porous material 103 to fill the space therebetween to formthe heat-resistant rubber layer 102. After the silicone rubber 131 hashardened the elastic fixing roller is removed from the mold.

Alternatively, the elastic fixing roller according to the firstembodiment of the present invention may be produced by first formingheat-resistant rubber layer 102 on the outer surface of roller core 101,and then covering layer 102 with the heat-resistant porous material 103.The porous material 103 is then impregnated with the liquid rubber 104and hardened. After the surface of the resultant roller is polished toimprove its roundness, the thin heat-resistant rubber coating 105 isformed using a liquid phase method.

The formation of coating 105 by the liquid phase method is carried outby applying, for example, a thin, self-adhesive coating of liquidsilicone rubber of room temperature vulcanizing (RTV), that hardens atroom temperature and is self-adhesive and possesses superior releasingproperties.

In summary, the elastic fixing roller described above is arranged sothat a first heat-resistant rubber layer is formed on the outer surfaceof a roller core, a second heat-resistant rubber layer reinforced by aheat-resistant porous material is formed on the outer surface of thefirst rubber layer, and a thin heat-resistant rubber layer severalhundred μm thick or less is formed as the outermost layer of the roller.The second rubber layer reduces the possibility that the outermostrubber layer will be damaged due to separating pawls or a thermistorand, thus, extends the life of the rubber roller.

The fixing roller disclosed in the Japanese Publication uses a porousmaterial of ethylene tetrafluoride resin impregnated with liquidsilicone rubber and is polished after hardening. However, the Shorehardness of the impregnated porous material after the liquid siliconerubber has hardened is more than 50 degrees. It was impossible to reducethe Shore hardness below 50 degrees by polishing or other methods.

Although a fixing apparatus having a wide nip width (the width of thecontact between the rollers) for fixing toner under as low a pressure aspossible is generally required, the use of a conventional fixing rolleris limited due to its Shore hardness.

According to the first embodiment of the present invention, it ispossible to produce an elastic fixing roller having a Shore hardness of30 degrees or less if the thickness of the heat-resistant porousmaterial is reduced. Furthermore, the thin outermost heat-resistantrubber coating provides a glossy outer surface on the elastic fixingroller making it extremely effective for color copying and likeprocesses requiring gloss.

Furthermore, where a silicone oil is used as a releasing agent to coatthe surface of the elastic fixing roller, the wetability/compatibilityof a silicone oil is increased so that the realeasing effect of thetoner or copy paper from the roller is increased.

For purposes of example only, the first embodiment of the presentinvention can be made according to the following specifications: Hollowmetal mold 130 is made of SUS304 grade stainless steel having an innerdiameter of 40 mm, a thickness of 5 mm, a length of 350 mm, and amirror-finished inner surface; roller core 101 is made of aluminumhaving an outer diameter of 34 mm, a thickness of 2 mm, and a length of320 mm; and metal core fitting 132 is made of SUS304.

To carry out the method of producing the fixing roller according to thefirst embodiment of the present invention, a porous tube of ethylenetetrafluoride resin (trade name POREFLON, made by SUMITOMO ELECTRICINDUSTRIES Co., Ltd.) having an outer diameter of 40 mm, a thickness of0.8 mm, a pore size of 10 μm, and a porosity of 85% was set inside thehollow metal mold, and the metal core coated with a primer was set atthe center of the mold. Liquid silicone rubber (trade name KE103, madeby SHIN-ETSU CHEMICAL Co., Ltd.) having a viscosity of 1100 c.s. waspoured between the metal core and the porous tube and hardened at 200°C. for one hour after defoaming. Thereafter, the resultant elasticfixing roller was removed from the mold.

The Shore hardness of the rubber roller described above wasapproximately 35 degrees, which was only about 20 degrees higher thanthe hardness of the KE103 itself. The thickness of the outermost thinfilm was 0.05-0.1 mm providing a mirrored surface.

Excellent picture quality was obtained using the aforementioned rolleras a heating roller in the fixing stage of a color copier as shown inFIG. 4 where reference numerals 123, 133, 134, 135, and 136 represent aheater, heating roller, pressing roller, contact roller, and web,respectively. A nip width of 4 mm between the heating and pressingrollers was sufficient.

For comparison purposes, the fixing roller disclosed in the JapanesePublication, in which a porous tube of ethylene tetrafluoride resin wasdisposed inside the roller, had a Shore hardness of 60 degrees and,therefore, provided insufficient nip width.

The elastic fixing roller according to the first embodiment of thepresent invention is superior to conventional rollers in several ways.First, use of the roller is less likely to wrinkle the copy paper. Inaddition, the rubber layer cannot be damaged by separating pawls or athermistor, thus extending the life of the roller. Further, the elasticfixing roller according to the present invention has superior releasingproperties due to its mirrored surface. Also, because the hardness ofthe roller is low, the picture quality obtained by the roller isexcellent.

FIGS. 5 and 6 illustrate a second embodiment of the present invention.FIG. 5 shows an elastic fixing roller having a continuous porous layer202 of fluorocarbon resin, containing 2-30 portions of inorganic fillerto enlarge its pore size, formed on the outer surface of roller core201. The core can be made of metal, ceramic, plastic, or the like. Theporous portions of layer 202 are impregnated with a heat-resistantliquid rubber 203, in which an inorganic filler of particle size nolarger than 5 μm and/or a releasing agent is added by 0.1-20 portions,and then hardened. Ethylene tetrafluoride resin having a porosity of70-95% and a pore size of 1-50 μm is preferably used as the fluorocarbonresin porous layer 202. It is further preferable to use liquid siliconerubber or fluororubber having a Shore hardness of 20-70 degrees and aviscosity of 10,000 c.s. or less as the heat-resistant liquid rubber203.

The elastic fixing roller described above provides many benefits. Thefluorocarbon resin exposed on the surface of the roller at apredetermined rate results in better toner releasing properties thanthat of rubber alone. Further, the elasticity of the roller prevents itfrom crushing the toner, allows sufficient heat conduction for properfixing, and prevents the copy paper from wrinkling. In addition, thetensile strentgh of the roller is higher than that of a conventionalrubber roller because the elastic fixing roller has a reinforcedarrangement of fluorocarbon resin fibers that form pores having a nettyarrangement extending into the rubber. This helps prevent damage to theroller caused by the separating pawls of a copying machine.

Also, the rubber hardness of the composite layer of the fluorocarbonresin and the elastic material is higher than that of the elasticmaterial taken alone. It is necessary to use an elastic material havinga Shore hardness lower than 15 degrees to make the rubber hardness ofthe composite layer less than 35 degrees. However, such rubber has lowtensile strength and poor heat-resistance so that the surface of therubber will begin to separate after thousands of copies are made whichlowers the picture quality of the copies and decreases the releasingproperties of the roller. On the other hand, if the Shore hardness ofthe composite layer exceeds 80 degrees, the nip width narrows whichtends to lower the degree to which the toner fixes to copy paper.

It is possible to improve roller performance by adding certain inorganicfillers and/or releasing agents to the liquid rubber. For example, toincrease the heat-resistance of the rubber, iron oxide red, carbonblack, or silica is added. A higher heat conductivity is achieved byadding graphite or metal powder to the liquid rubber. To increaseelectrical conductivity, carbon black or metal powder can be added.Silicon oil is added to the liquid rubber to increase the releasingproperties of the rubber.

The fixing roller described in the Japanese Publication is disclosed ashaving a pore size of about 10 μm and a porosity of ethylenetetrafluoride resin of at least 90%, so that, at most, five portions ofan inorganic filler and/or a releasing agent could be added to theliquid rubber and it takes a considerably long time for the liquidrubber to impregnate the resin.

According to the second embodiment of the present invention, aninorganic filler also is added to the fluorocarbon resin by 2-30portions to increase pore size and porosity thereby making it possibleto increase the quantity of the filler and/or releasing agent to beadded to the liquid rubber. This improves the roller characteristics andreduces the time necessary to impregnate the liquid rubber. When lessthan two portions of inorganic filler was added to the fluorocarbonresin, its pore size and porosity did not significantly increase. Use ofmore than 30 portions of inorganic filler made it impossible to producethe porous material. On the other hand, when the quantity of the fillerand/or releasing agent to be added to the liquid rubber is less than 0.1portions, no satisfactory effect could be obtained; when it exceeded 20portions, it was impossible to impregnate the porous material.

As described above, the elastic fixing roller according to the secondembodiment of the present invention used in a fixing apparatus of acopying machine or the like, achieves excellent results which aredifficult to obtain using conventional rollers. The roller causes littlewrinkling of the copy paper and the picture quality is excellent. Therubber layer will not be damaged by separating pawls, a thermistor, orthe like, thus extending the life of the roller. Further, the timenecessary to raise the temperature of the roller and to impregnate itwith liquid rubber can be reduced.

Referring to FIGS. 5 and 6, examples of the second embodiment of thepresent invention was made according to the following specifications:

An aluminm roller core 201 has a degreased surface, a roller diameter of59.8 mm, and a length of 320 mm. A porous tube 202 of ethyleneteraflouride resin, having a thickness of 0.8 mm, a porosity of 90% anda pore size of 15 μm, is formed by inpregrating ten portions of graphiteinto a PTFE resin, extended and baked from 100% to 800% in alongitudinal direction and from 100% to 200% in a radial direction. Thealuminum roller core 201 is covered with the porous tube 202.

Porous tube 202 was impregnated with liquid silicone rubber 203 having aviscosity of 5,000 c.s. and added along with 5 portions of graphitehaving a particle size of 0.5 μm and 10 portions of silicone oil havinga viscosity of 100 c.s. After hardening, the surface of porous tube 202was polished to obtain an elastic roller having an outer diameter of60.8 mm and was provided with an inverted crown of 100 μm.

For testing purposes, the elastic roller of FIG. 5 was used as a heatingroller 210 of a fixing apparatus, as shown in FIG. 6, attached to acopying machine capable of delivering 50 copies per minute using A4paper (paper size No. 4 of series A paper under Japanese standards). Aweb 221 of NOMEX impregnated with a small quantity of silicone oil wasused as a cleaning member on the outer surface of the heating roller210. As shown in FIG. 6, web 221 rotates in a direction opposite to thatof heating roller 210. In this case, the temperature rising time of theroller was about three minutes. After 200,000 continuous copies, theroller was not damaged by the separating pawls 218 and was still insatisfactory condition for further use.

For comparison purposes, PFTE resin added with no filler was extendedand baked under the same conditions as those of described in the firstexample above. The porous tube had a thickness of 0.8 mm, a porosity of85%, and the pore size was 5 μm. The tube was impregnated with liquidsilicone rubber filled with graphite particles of 0.5 μm. In this caseit was impossible to impregrate the tube with more than one portion ofliquid silicone rubber. The temperature rising time of the roller inthis case was about 3.5 minutes.

In a second example, a roller core having the same roller diameter asthat of the first example was covered with a porous tube of ethylenetetrafluoride resin so that PTFE resin added with twenty portions ofiron oxide red was extended and baked from 100% to 800% in alongitudinal direction and from 100% to 300% in a radial direction. Theporous tube had a thickness of 0.5 mm, a porosity of 90% and a pore sizeof 15 μm. The porous tube was impregnated with liquid silicone rubberhaving a viscosity of 5,000 c.s. added with five portions of iron oxidered so that the thickness of the porous tube coated with the siliconerubber was 0.5 mm larger than the original porous tube. The surface ofthe outermost silicone rubber layer was polished to produce a roller inwhich the ethylene tetrafluoride resin porous tube was exposed on thesurface of the roller.

For testing purposes, the roller was used as a heating roller in thesame fixing apparatus as that of the first example. Any damage wascaused, if at all, by the separating pawls 218, so that excellentpicture quality was obtained up to 400,000 copies.

FIGS. 7 and 8 illustrate a third embodiment of the present invention. InFIG. 7, the elastic fixing roller is provided with a continuous porouslayer 302 of fluorocarbon resin surrounding the outside of a roller core301 made of metal, ceramics, plastics, or the like. Porous layer 302 isimpregnated with heat-resistant liquid rubber 303, hardened, and thenpolished to obtain the correct roundness. A thin liquid rubber coating304 having a low viscosity is applied and hardened to reduce theroughness of the surface thereby making the surface glossy to increasethe toner releasing properties of the roller. This roller isparticularly effective for use in color copying.

Taking into consideration the releasing properties and handling of theroller, it is preferable to use liquid silicone rubber which hardens atroom temperature as the heat-resistant liquid rubber. However, theliquid silicone rubber used for surface coating is not always requiredto have the same grade as that used to impregnate the porous rubberlayer.

It is also preferable to use liquid silicone rubber having a Shorehardness of 80 degrees or less after hardening and a viscosity of100,000 c.s. or less to impregnate layer 302. The liquid silicone rubberforming the outermost layer preferably has a Shore hardness of 100degrees or less after hardening at room temperature and a viscosity of10,000 c.s. or less.

In this arrangement, for example, a layer of woven or nonwoven polyamidefabric or the like or a layer of carbon fibers may be substituted forthe continuous porous layer of fluorocarbon resin.

Again, excellent results can be obtained using the roller justdescribed. The surface of the roller is glossy which improves itsreleasing properties and elasticity. Further, the tensile strength ofthe roller is higher than that of conventional rubber rollers. Thereinforced arrangement of fluorocarbon resin fibers form pores that havea netty arrangement extending into rubber which prevents the separatingpawls from damaging the roller. However, the pawls may damage the rollerif the outermost heat-resistant rubber layer is too thick and,therefore, the outermost layer is preferably 0.2 mm thick or less,ideally several tens μm thick, so that the uneven flat portion of theroller becomes an even polished surface. Such a surface is obtained byapplying liquid rubber of the solvent dilution type, having lowviscosity and a superior adhesive property, to the surface by means of aroller or the like.

The third embodiment of the present invention was made using an aluminumcore having a degreased surface and a roller diameter of 40 mm. A lengthof 32 mm of the core was made adhesive and coated with a porous tube ofethylene tetrafluoride resin having a thickness of 2.5 μm, a porosity of80%, and a pore size of 2 μm. The porous tube was impregnated withtwo-part liquid silicone rubber (trade name KE 103, made by SHIN-ETSUCHEMICAL Co., Ltd.) and then hardened at room temperature. The surfaceof the porous tube was then polished to an outer diameter of 44 mm and asurface roughness of 10 μm. The roller surface was then coated withone-part liquid silicon rubber (trade name S-COAT 58, made by SHIN-ETSUCHEMICAL Co., Ltd.), approximately 20 μm thick and hardened at roomtemperature. The surface roughness was about 2 μm creating a glossysurface. The Shore hardness of the rubber roller was 60 degrees atordinary temperatures and 45 degrees when the roller was heated to 200°C.

Referring to FIG. 8, the roller described above was used as a heatingroller 305 in a fixing apparatus which was attached to a full-colorcopying machine capable of producing ten copies per minute using A4paper. Reference numerals 306, 308, and 309 designate a pressing roller,a contacting roller, and a heater, respectively. A web 307 of NOMEXimpregnated with a small quantity of silicone oil was used as a cleaningmember on the outer surface of roller 305. Web 307 rotates in adirection opposite to that of roller 305.

Using this setup, excellent picture quality was attained with no offsetup to 20,000 copies. For comparison test purposes, the same roller asthat of the foregoing example was used in a color copying machine exceptthat the surface was not coated with one-part liquid silicone rubber butonly polished. In that case, the picture quality of the color copies wasless glossy, and after several tens copies, offset occurred preventingfurther copying.

FIGS. 9 and 10 illustrate a fourth embodiment of the present invention.In FIG. 9, a woven or nonwoven fabric layer 402 of heat-resistantfibers, for example, fluorocarbon resin fibers, carbon fibers, metalfibers, polyamide fibers, or the like, is provided on the outer surfaceof a roller core 401 made of either metal, ceramics, plastics, or thelike. Fabric layer 402 is then impregnated with heat-resistant liquidrubber 403 and hardened.

In this embodiment, silicone rubber of fluororubber having highviscosity is used as the heat-resistant liquid rubber. The roller can beeasily constructed if molding is performed using a liquid siliconerubber injection molding system (LIMS).

Generally, an inorganic filler such as iron oxide red, silica, or thelike is added to the liquid rubber to raise the heat-resistance andelectrical conductivity of the roller, and silicone oil is added to theliquid rubber to raise its releasing properties.

In this embodiment, damage due to separating pawls or a thermistor of acopying machine is lessened and, thus, roller life is prolonged, becausethe rubber is reinforced by the woven or nonwoven fabric of fluorocarbonresin or by the conductive woven or nonwoven fabric of carbon, metal, orthe like.

In the fixing roller disclosed in the Japanese Publication in which theporous ethylene tetrafluoride resin is impregnated with liquid siliconerubber and then polished after hardening, the viscosity of the liquidsilicone rubber and the particle size and quantity of the filler islimited. No such limitations are present in the elastic fixing rolleraccording to the fourth embodiment of the present invention.

An example of the fourth embodiment of the present invention was madeusing a metal core having a degreased surface and a roller diameter of40 mm. A length of 320 mm of the core was coated with a silicone rubberprimer and dried. A fluorocarbon resin, nonwoven fabric layer, 3 mmthick, was formed on the outer surface of the metal core and impregnatedwith liquid silicone rubber (trade name KE 1331, made by SHIN-ETSUCHEMICAL Co., Ltd.) having a viscosity of 30,000 c.s., a Shore hardnessof 40 degrees, and a tensile strength of 35 kg/cm², and then hardened at200° C. for five hours. The surface of the resultant outer layer waspolished by an external cylindrical grinding machine to an outerdiameter of 45 mm. The surface has a 10:1 ratio of silicone rubber andfluorocarbon resin fibers. The coating layer of the roller had a Shorehardness of 70 degrees and a tensile strength of 60 kg/cm².

Referring to FIG. 10, the roller was used as a heating roller 404 in afixing apparatus which was attached to a copying machine capable ofmaking 50 copies per minute of A4 paper. Reference numerals 405, 406,and 407 designate a pressing roller, a web, and a contacting roller,respectively. A web 406 of NOMEX impregnated with a small quantity ofsilicone oil was used as a cleaning member on the outer surface of theheating roller 404. As shown in FIG. 10, web 406 rotates in a directionopposite to that of heating roller 404. Once again, excellent resultswere obtained using the fourth embodiment of the present invention. Upto 200,000 copies, the roller was undamaged by the separating pawls andno wrinkling of the paper occurred, producing excellent picture quality.

FIGS. 11 and 12 illustrate a fifth embodiment of the present invention.FIG. 11 shows a heat-resistant rubber layer 502 formed on the outside ofa roller core 501 made of metal, ceramics, plastics, or the like. Aheat-resistant rubber layer 504 reinforced by heat-resistant porousmaterial or fibers 503 is formed on the outer surface of rubber layer502.

In this embodiment, a porous material or a woven or nonwoven fabric offluorocarbon resin may be used if the releasing properties of thesurface is an important consideration, and a woven or nonwoven fabric ofconductive fibers such as carbon, metal, or the like may be used ifelectrical conductivity is required. A liquid silicone rubber having aviscosity of 100,000 c.s. or less is generally used as theheat-resistant rubber layer. Further, an even higher performance rollercan be obtained if an inorganic filler such as iron oxide red, silica,or the like is added into the liquid rubber to further raise theheat-resistance of the roller or if a releasing agent such as siliconeoil or the like is added to raise the releasing properties of theroller. The surface of the elastic fixing roller is polished to improveits roundness and to expose a mixed layer on the outer surface of theroller.

In this embodiment, as in the other embodiments, the life of the rolleris prolonged. That is because the rubber is reinforced by the porousmaterial or the woven or nonwoven fabric of fluorocarbon resin, or theconductive fabric or nonwoven fabric of carbon, metal, or the like,which reduces the damage caused by the separating pawls or thermistor ofa copying machine.

In the fixing roller disclosed in the Japanese Publication, in which aporous material of ethylene tetrafluoride resin is impregnated withliquid silicone rubber and polished after hardening, has a Shorehardness of at least 50 degrees. It was impossible to reduce the Shorehardness below 50 degrees by polishing or other methods. Therefore, in afixing apparatus in which the nip is widened so that the toner is fixedunder as low a pressure as possible, which is a current tendency, theuse of the fixing roller is limited. According to the fifth embodimentof the present invention, however, it is possible to produce an elasticfixing roller having a Shore hardness of 30 degrees or less by reducingthe thickness of the heat-resistant porous material.

The fifth embodiment of the present invention can be made using the samemold and core specifications disclosed in connection with the firstembodiment of the present invention and shown in FIG. 3.

To carry out the method of producing this embodiment, for example, aporous tube of ethylene tetrafluoride resin having an outer diameter of40 mm, a thickness of 0.4 mm, a pore size of 10 μm, and porosity of 85%was set inside a hollow metal mold. A metal core, coated with a primer,was set at the center of the mold using metal core fittings. Liquidsilicone rubber (trade name KE 106, made by SHIN-ETSU CHEMICAL Co., Ltd)having a viscosity of 5,000 c.s., was poured between the metal core andthe porous tube and hardened at 200° C. for one hour after defoaming.Thereafter, the roller was removed from the mold.

The surface of the rubber roller was polished to an outer diameter of39.5 mm so that a mixed layer of ethylene tetrafluoride resin andsilicone rubber is exposed on the surface. The Shore hardness of therubber roller was about 45 degrees, only about five degrees higher thanthat of KE 106 itself.

For test purposes, the fifth embodiment of the rubber roller was used asa heating roller 505 of a plain paper copier (PPC) as shown in FIG. 12.Reference numerals 507, 508, and 509 designate a contacting roller, aweb, and a heater, respectively. A sufficient nip width of 4 mm betweenheating roller 505 and pressing roller 506 was provided. Using thatdevice, a copy having excellent picture quality was obtained with hardlyany wrinkles. In addition, the rubber layer was not damaged, thusprolonging the life of roller.

For comparison purposes, a fixing roller as disclosed in the JapanesePublication, in which a porous tube of ethylene tetrafluoride resinexisted up to the inside of the fixing roller, the Shore hardness was 70degrees and therefore sufficient nip width could not be obtained.

Although the present invention has been described in connection withwhat is considered to be the preferred embodiments, it should beunderstood by those skilled in the art that the invention is not limitedto only those disclosed embodiments, but may include variousmodifications without departing from the scope or spirit of theinvention.

We claim:
 1. An elastic fixing roller for use in a fixing stage of afixing apparatus such as a copying machine, comprising:a roller core; alayer provided on the outer surface of said roller core made of areinforcing heat-resistant material impregnated with a reinforcingheat-resistant elastic material that has been hardened afterimpregnation; and a thin film of a heat-resistant elastic materialprovided on the outer surface of said layer.
 2. An elastic fixing rolleras set forth in claim 1, wherein said reinforcing heat-resistantmaterial is a porous fluorocarbon resin.
 3. An elastic fixing roller asset forth in claim 1 wherein said reinforcing heat-resistant material iseither a woven or nonwoven fabric.
 4. An elastic fixing roller as setforth in claim 3, wherein said fabric is made of carbon fibers.
 5. Anelastic fixing roller as set forth in claim 1, wherein saidheat-resistant elastic material is liquid silicone rubber having a Shorehardness no higher than 80 degrees after hardening and having aviscosity no higher than 100,000 c.s.
 6. An elastic fixing roller as setforth in claim 1, wherein said thin film is no thicker than 0.2 mm. 7.An elastic fixing roller as set forth in claim 1, wherein saidheat-resistant elastic material is liquid silicone rubber having a Shorehardness no higher than 100 degrees after hardening at room temperatureand having a viscosity no higher than 10,000 c.s.